Russia's Sukhoi Aircraft says that it is unable to do anything to stop China from testing and manufacturing a copy of its Su-33 carrier-based fighter.
Beijing was keen to buy several dozen Su-33s earlier this decade as part of its plans to develop a deep-sea naval capability, but the deal never went through.
Instead, industry sources believe that it bought a Su-33 prototype from Ukraine and started using that as a prototype for its development, which has been tagged the Shenyang J-15. The first flight of the aircraft is believed to have taken place in June.
"There are licence agreements in place when countries buy our aircraft and it is illegal to produce a copy of it without getting our agreement," says Sukhoi's chief executive Mikhail Pogosyan. He adds that his company has "intelligence" about the Chinese aircraft, but says that there is little that can be done.
"We are always looking very carefully at what the competition is doing. What I can stress is that no copy is equal to the original, it will always be inferior to the original product. They do not have the technological capabilities that we have."
China, which used to depend on Russia for many of its military requirements, is going ahead with various programmes to develop indigenous aircraft that bear a close resemblance to its former supplier's products. It is also keen to become a supplier and potentially compete with Russia in the market, especially in the third world.
"We always welcome competition, even if it is not righteous competition, and we respect it," says Pogosyan. "But I am 100% sure that we have the products that will have an edge and a market."